Obesity: A Scientific Perspective

June 5, 20080 Comments1223 Views

Obesity is presence of excess quantity of body fat, more than scientifically acceptable limit. Deposition of excess food as body fat is a physiological response of the body developed during the time of evolution to overcome food shortage during lean periods. But presently it is causing serious problem because of easy access to food and sedentary lifestyle. Obesity is most commonly measured in terms of BMI (body mass index). BMI is calculated by the following formula, body weight is divided by height in meter square, (body weight/ height2). Body height is in meters. Obesity is defined as BMI more than 30. For normal people BMI is from 18.5 to 30. BMI below 18.5 is taken as underweight. Risk of cardiovascular disease is minimal at this range of BMI. There are other formulas for measurement of obesity. This formula of calculating obesity by BMI is also not foolproof, because if a person is very muscular like body builders, he may have very little body fat but his BMI may be >30. We can not call him obese. Overweight can be called when BMI is form 25 to 30.

Prevalence of obesity: obesity is more common problem in industrialized countries. For example in USA prevalence of obesity was about 30% in the year 2000, and it is increasing. In the year 1975 to 1980 it was 15%. In 2000 as many as 64% of adult population above 20 years were overweight, as calculated by BMI of >25.

Now the burning question is do the obese eat more than the lean?

Answer to this question is not simple. This question has created much debate. There are methodological difficulties in determining food intake. Some of the obese individuals claim they eat less, and these claims are supported by the results of food intake questionnaires. However, it is now established that the average energy expenditure increases with obesity, due to the fact that metabolically active lean tissue mass increases. According to law of thermodynamics, therefore an obese person must eat more to maintain his increased body weight. But certain people who are predisposed to obesity due to there genetic structure, may develop obesity without absolute increase in calorie consumption.

What is the state of energy expenditure in obesity?

The average daily energy expenditure is more in obesity, due to metabolically active extra tissue mass. But when weight is lost the energy expenditure is reduced and for maintenance of body weight less energy is used than it would have been in case of lean person at that weight. This is one of the main reasons why obese people find it difficult to maintain body weight after bringing down body weight to normal.

Causes of obesity: Most important of obesity is eating more food than required to maintain ideal body weight. Next important cause is genetics. There are also certain medical conditions where body weight increases for example, diabetes.